Exhaust gas recirculation (EGR) is commonly used for NOx emission control in an internal combustion engine. Without cooling, EGR may increase intake temperatures above a level that adversely affects engine operation. As a way of dealing with this issue, EGR coolers using engine coolant as a low temperature media have been used to cool EGR gas temperatures.
Some diesel engines may have large EGR cooling demands due to the large amounts of EGR needed to meet NOx emissions. In such engines, using the engine coolant alone to cool the EGR may either be inadequate or require an excessively large EGR cooler that exceeds available package space in an engine compartment. As an alternative, a standard-sized EGR cooler may be followed by an additional EGR cooler that uses a lower temperature coolant to further cool the EGR. However, one issue with the above solution is potential fouling inside the lower temperature EGR cooler when more hydrocarbons and vapor are deposited or condensed when the EGR is cooled to a lower temperature by the additional EGR cooler.
To at least partially address the issue of providing adequate cooling to engines while avoiding EGR fouling, an EGR cooling system is provided. The EGR cooling system comprising a plurality of EGR coolers configured to cool the EGR to a plurality of successively lower temperatures, where at least one of the plurality of EGR coolers includes a finned EGR cooler that comprises a plurality of channels for dissipating heat in the EGR, the plurality of channels increasing heat transfer surface area while having sufficient fin spacing to avoid clogging. The EGR cooling system may further comprise a catalyst configured to remove particle matters and/or hydrocarbons from the EGR, the catalyst positioned upstream of at least one of the plurality of EGR coolers.
In this way, the engine may provide high levels of EGR cooling, while addressing issues of EGR fouling and engine packaging. Specifically, by providing a plurality of EGR coolers that cool the EGR to successively lower temperatures, it may be possible to meet the EGR cooling demand of a high load engine without drastically increasing the size of the EGR cooling system. Further, by positioning a catalyst upstream of at least one of the plurality of EGR coolers, it may be possible to reduce EGR fouling. Likewise, by using an EGR cooler with appropriate fin spacing, it may be possible to increase heat transfer surface area within the EGR cooler package space and further increase heat dissipation to the coolant but avoid clogging due to hydrocarbon deposit build up.